NCERT Solutions Curiosity Chapter 4 Projects and further exploration — Learning further

Book page 76 & 77 Updated on2026-09-05

Q1.

Using 3–4 different magnets, try to lift steel pins or U-clips and check which magnet picks up the largest number of pins. Discuss with your friends why different magnets might have picked up different numbers of pins.

Answer

How to do it fairly: use the same heap of identical pins, dip one pole of each magnet into the heap in the same way, lift straight up, and count what hangs on. Repeat three times for each magnet and take the largest count.

Magnet	Trial 1	Trial 2	Trial 3	Best count
Small bar magnet	6	7	6	7
Large bar magnet	12	11	13	13
U-shaped magnet	18	17	19	19
Ring magnet	9	10	9	10

Sample answer (your own numbers will differ): the U-shaped magnet lifted the most pins and the small bar magnet the fewest.

Why different magnets pick up different numbers:

Strength of the magnet. Some magnets are made of stronger materials and were magnetised more thoroughly.
Size. A bigger magnet of the same material is usually stronger.
Shape. In a U-shaped magnet both poles face the same way and pull on the same heap together, so it beats a bar magnet of similar size.
Age and treatment. A magnet that has been dropped, hammered, heated or stored carelessly loses strength.
Where you touch the heap. A pole picks up many pins, the middle picks up hardly any — so always use a pole.

Tip: Counting pins is a real way of measuring magnet strength. Record your table in your notebook and test the same magnets again after six months — a magnet stored without its keeper will have grown weaker.

Q2.

Make a toy ‘Hopping Frog’ as a combined class activity with the help of your teacher. For constructing the toy, fix ring magnets in an alternate North-South fashion along the length of a scale using glue (Fig. 4.18a). Paint a frog on paper, cut along the outline and glue a ring magnet at its base. Take a transparent, flexible plastic strip (Fig. 4.18a) of a smaller size and glue it to the ring magnet which is attached to the frog. When you slide the plastic strip (with frog) over the scale (Fig. 4.18b), you can observe the frog hopping.

Answer

What you need: a wooden or plastic scale, 6–8 ring magnets, glue, a thick paper frog, and a small transparent flexible plastic strip.

Steps:

Glue the ring magnets in a row along the scale, alternating their faces — the first with its North face up, the next with its South face up, the next North, and so on.
Colour and cut out the paper frog and glue one ring magnet at its base.
Glue the flexible plastic strip to that magnet so the frog can spring up and down a little.
Slide the strip with the frog slowly along the scale and watch the frog hop.

Why the frog hops: as the frog's magnet passes over a magnet whose facing pole is like its own, it is repelled and jumps up. Over the very next magnet the facing pole is unlike, so it is attracted and comes down. Because the magnets on the scale alternate N, S, N, S…, the frog gets push–pull–push–pull one after another and appears to hop along. The springy plastic strip lets it bounce instead of staying stuck.

Tip: Mark the top face of each ring magnet with a dot as you glue it, so you can check that the sequence really alternates. If two neighbouring magnets are put the same way up, the frog will skip a hop at that point.

Q3.

Find out about the Maglev Train and try to make its model.

Answer

What a Maglev train is: “Maglev” is short for magnetic levitation. The train does not roll on wheels — it floats a few centimetres above the guideway and is pushed forward by magnets.

Job	How magnets do it
Lifting the train	Strong magnets on the train and on the track have like poles facing, so they repel and the train rises
Guiding it on the line	Side magnets keep pushing it back to the centre if it drifts
Moving it forward	The track's magnetism is switched on and off in a wave, so the train is pulled forward and pushed from behind

Why it is fast and quiet: nothing touches the track, so there is almost no friction. Maglev trains reach speeds above 400 km/h, run very smoothly and need little repair. Such trains run in Japan, China and South Korea. The Shanghai Maglev is the best-known one.

A simple model you can make:

Fix two rows of ring or strip magnets along a wooden channel, all with the same pole facing up.
Glue matching magnets under a light cardboard “train”, again all with the same pole facing down — the same pole as on the track.
Place the train on the channel. Like poles face each other, so the train floats.
Give it a gentle push; it glides along the channel. Low walls on either side keep it from slipping off.

Check it yourself: Turn the cardboard train upside down and put it back. It will now stick to the track instead of floating — proof that the floating came from repulsion between like poles.

Q4.

Try to find out why there is a need to make magnets of different shapes.

Answer

Because the shape decides where the poles are — and different jobs need the poles in different places.

Shape	Where its poles are	Why that shape is useful
Bar magnet	At the two ends, far apart	Best for learning about poles, and for hanging freely to find directions
U-shaped (horseshoe)	Two tips side by side, facing the same way	Both poles pull on the same object, so it lifts much more — used in cranes and holders
Ring magnet	On the two flat faces	Slides over a rod or shaft — used in loudspeakers, motors and the hopping-frog toy
Disc magnet	On the two flat faces	Thin and flat — fits inside pencil boxes, purses, fridge stickers and cupboard catches
Cylindrical magnet	At the two circular ends	Fits into narrow holes and tubes — used in latches and sensors
Needle shaped	At the two sharp ends	Light and free to turn on a pin — the compass needle
Spherical magnet	At two opposite points on the ball	Rolls freely — used in toys and puzzles

The rule behind all of it: whatever the shape, a magnet still has exactly two poles, in a pair. Shape changes only where the poles sit and how far apart they are — and that is precisely what makes one magnet right for a fridge door and another right for a compass.

Q5.

Collect information related to the use of magnets in the field of medicine.

Answer

Magnets are used in hospitals far more than most people imagine. Here is what a class survey of newspapers, books and a hospital visit would turn up.

Use in medicine	What it does
MRI scan (Magnetic Resonance Imaging)	A very powerful magnet lets doctors see the brain, spine, knees and other soft parts of the body clearly — without any surgery and without X-rays
Removing iron splinters	A tiny iron chip that has gone into the eye or a wound can be drawn out with a small magnet instead of cutting
Magnets in hearing aids and cochlear implants	Hold the outer part in place on the head and help carry sound signals
Magnetic therapy belts and mats	Sold for pain in the knee, back and joints. Their benefit is not well proved by science — treat such claims carefully
Separating cells and proteins in laboratories	Tiny magnetic beads are used to pull out particular cells from a blood sample for testing
Guiding medicines	Newer research uses magnets to steer medicine to just the diseased part of the body, so that less of it reaches the healthy parts

Important safety note: because an MRI magnet is enormously strong, patients must remove all iron and steel objects — hairpins, keys, coins, watches — before entering the room. People with a heart pacemaker or a metal implant cannot always have an MRI. This is the same lesson as the chapter's warning to keep magnets away from mobile phones, only on a much larger scale.

How to present your findings: make a chart with three columns — where the magnet is used, what it does, and the property of magnets it depends on (attraction of iron, or the magnetic effect passing through the body). Add a picture of an MRI machine cut from a newspaper.

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